Display device

ABSTRACT

The present invention provides an active matrix type display device having a high aperture ratio and a required auxiliary capacitor. A source line and a gate line are overlapped with part of a pixel electrode. This overlapped region functions to be a black matrix. Further, an electrode pattern made of the same material as the pixel electrode is disposed to form the auxiliary capacitor by utilizing the pixel electrode. It allows a required value of auxiliary capacitor to be obtained without dropping the aperture ratio. Also, it allows the electrode pattern to function as a electrically shielding film for suppressing the cross-talk between the source and gate lines and the pixel electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/982,255, filed Dec. 30, 2010, now allowed, which is a continuation ofU.S. application Ser. No. 12/610,450, filed Nov. 2, 2009, now U.S. Pat.No. 7,863,618, which is a divisional of U.S. application Ser. No.11/382,412, filed May 9, 2006, now U.S. Pat. No. 7,646,022, which is acontinuation of U.S. application Ser. No. 10/196,878, filed Jul. 15,2002, now U.S. Pat. No. 7,046,313, which is a continuation of U.S.application Ser. No. 09/546,636, filed Apr. 7, 2000, now U.S. Pat. No.6,421,101, which is a continuation of U.S. application Ser. No.08/922,951, filed Sep. 3, 1997, now U.S. Pat. No. 6,115,088, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 08-253817 on Sep. 4, 1996, all of which are incorporated byreference

BACKGROUND OF THE INVENTION

The invention disclosed in the present specification relates to astructure of a liquid crystal display or a fabrication method thereof.

DESCRIPTION OF RELATED ART

There has been known a fiat panel display typified by a liquid crystaldisplay. In a transmission type liquid crystal display having a mode ofoptically modulating light which has passed through a liquid crystalpanel by the liquid crystal panel, light shielding means called a blackmatrix is required in order to clearly define a profile of pixels. Inconcrete, it is necessary to cover the peripheral portion of a pixelelectrode by a light shielding frame. Such a black matrix plays animportant role in displaying fine motion pictures in particular.

However, the black matrix has a demerit that it reduces an effectivearea of a pixel (this rate will be referred to as an aperture ratio) anddarkens the screen.

It is being tried to utilize the flat panel display in low powerconsumption type portable equipments such as a portable video camera anda portable information terminal in recent years.

What comes into question here is the low power consumptioncharacteristic which is required for such portable equipments. That is,it is necessary to reduce the power consumption used for displaying thescreen.

In case of the transmission type liquid crystal display, a method how toreduce power consumed by a back-light for illuminating from the back ofthe liquid crystal panel comes into question. The power consumption ofthe back-light may be reduced by reducing brightness of the back-lightby increasing the aperture ratio of the pixel.

Meanwhile, in case of the liquid crystal display, it is necessary todispose a capacitor called an auxiliary capacitor in order to supplementa capacity which liquid crystal has in each pixel. This auxiliarycapacitor has a function of holding information (which corresponds to aquantity of charge), which has been written to a pixel electrode andwhich is rewritten by a predetermined time interval, until it isrewritten in the next time. Flickers or nonuniformity of color (which isactualized specially in displaying in color) occurs in the display whenthe value of the auxiliary capacitor is small.

However, the provision of the auxiliary capacitor in each pixel alsobecomes a factor of dropping the aperture ratio of the pixel, similarlyto the case of disposing the black matrix.

SUMMARY OF THE INVENTION

As described above, the disposition of the black matrix and theauxiliary capacitor for the purpose of increasing the image qualitybecomes the factor of dropping the aperture ratio of the pixel. The dropof the aperture ratio invites a drop of the image quality in anothersense.

That is, it is contradictory to request a clear image to be displayed(by the effect of the black matrix) and to obtain a bright image (byincreasing the aperture ratio).

It is also contradictory to suppress the flickers and nonuniformity ofcolor in the display (by the effect of the auxiliary capacitor) and toobtain a bright image (by increasing the aperture ratio).

Accordingly, it is an object of the invention disclosed in the presentspecification to provide a technology for solving the above-mentionedcontradictory requests.

According to one of the invention disclosed in the presentspecification, an active matrix type display device comprises anelectrode pattern made of a conductive film disposed between source andgate lines and a pixel electrode; and an auxiliary capacitor formedbetween the electrode pattern and the pixel electrode.

According to another invention, an active matrix type display devicecomprises an electrode pattern made of a conductive film disposedbetween source and gate lines and a pixel electrode; an edge of thepixel electrode is disposed so as to overlap with the source and gatelines; and an auxiliary capacitor is formed between the electrodepattern made of the conductive film and the pixel electrode.

In the arrangements of the two inventions described above, the electrodepattern made of the conductive film functions as a shield film forelectrically shielding the source and gate lines from the pixelelectrode.

A structure of a still other invention is an active matrix type displaydevice in which an electrode pattern made of a conductive film isdisposed so as to cover source and gate lines.

In the structure described above, the electrode pattern made of theconductive film overlaps partially with the pixel electrode to form anauxiliary capacitor. Further, the electrode pattern made of theconductive film functions as a shield film for electrically shieldingthe source and gate lines from the pixel electrode.

One concrete example of the invention disclosed in the presentspecification is characterized in that an electrode pattern 106 made ofthe same material as a pixel electrode 107 is disposed between a sourceline 105 and a gate line 104 and the pixel electrode 107 to form anauxiliary capacitor between the electrode pattern 106 and the pixelelectrode 107 as its pixel structure is shown in FIG. 1.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an active matrix circuit in accordance with theembodiment 1 of the present invention;

FIG. 2 is a plan view of the active matrix circuit in accordance withthe embodiment 1 of the present invention;

FIG. 3 is a plan view of the active matrix circuit in accordance withthe embodiment 1 of the present invention;

FIG. 4 is a plan view showing a fabrication step of the active matrixcircuit in accordance with the embodiment 1 of the present invention;

FIG. 5 is a plan view showing a fabrication step of the active matrixcircuit in accordance with the embodiment 1 of the present invention;

FIG. 6 is a plan view showing a fabrication step of the active matrixcircuit in accordance with the embodiment 1 of the present invention;

FIG. 7 is a plan view showing a fabrication step of the active matrixcircuit in accordance with the embodiment 1 of the present invention;

FIG. 8 is a plan view showing a fabrication step of the active matrixcircuit in accordance with the embodiment 1 of the present invention;

FIGS. 9A through 9D are section views showing a fabrication step of theactive matrix circuit in accordance with the embodiment 1 of the presentinvention;

FIG. 10 is a section view showing a fabrication step of the activematrix circuit in accordance with the embodiment 1 of the presentinvention; and

FIG. 11 is a section view showing a fabrication step of the activematrix circuit in accordance with the embodiment 2 of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

FIGS. 1 through 3 show the structure of the present embodiment. FIGS. 1through 3 are enlarged plan views showing part of one pixel of an activematrix type liquid crystal display.

FIGS. 1 through 3 show the same part. The structure thereof will beexplained with reference to FIG. 1 at first. In FIG. 1, a pattern 101constitutes an active layer of a thin film transistor. The active layer101 is made of a crystal silicon film.

A reference numeral 102 which is part of the active layer 101 is aregion called as a drain region. A reference numeral 103 is a regioncalled as a source region. These regions are N-type in case of N-channeltype and are P-type in case of P-channel type.

A pattern 104 is a gate line. Regions in the active layer 101 at thepart where the gate line 104 overlaps with the active layer 101 arechannel regions. Regions where the gate line 104 overlaps with theactive layer 101 function as gate electrodes.

A source line 105 contacts with the source region 103 via a contact 111.

A vertical positional relationship between the active layer 101 and thegate line 104 is as follows. That is, a gate insulating film not shownis formed on the active layer 101 and the gate line 104 is formedthereon.

An interlayer insulating film not shown is formed on the gate line 104and the source line 105 is formed thereon.

A hatched region 106 is an electrode pattern made of ITO for forming acapacitor. This electrode pattern is latticed when seen from the pointof view of the whole active matrix region. The electrode pattern 106made of ITO for forming the capacitor is constructed so as to be kept atan adequate constant potential (reference potential). In concrete, it isconstructed so as to contact with an electrode of a counter substrate(this electrode is connected with a counter electrode) at the edge of anactive matrix circuit not shown. Thus, it is arranged so that itspotential is kept same with the counter electrode.

The shape of the electrode pattern 106 for forming the auxiliarycapacitor is not limited only to that shown in FIG. 1. Because theelectrode pattern 106 is made of ITO (or an adequate conductive film),it may be shaped with a large degree of freedom.

The pattern 107, made of ITO, constitutes the pixel electrode. The edgeof this pattern 107 is indicated by a broken line 108. That is, the edgeof the pixel electrode 107 is what a part thereof overlaps with thesource line 105 and the gate line 104.

FIG. 2 is a view in which the pattern of the pixel electrode 107 ishighlighted as a hatched part. That is the region indicated by the slantlines is the pixel electrode 107 in FIG. 2.

The pixel electrode 107 is formed on a second interlayer insulating film(not shown) which is formed on the electrode pattern 106 made of ITO forforming the capacitor.

As shown in FIG. 1, the pixel electrode 107 contacts with the drainregion 102 of the active layer pattern 101 via a contact 110.

As it is apparent from FIGS. 1 and 2 (FIG. 2 in particular), the pixelelectrode 107 is disposed so that its edge overlaps with the gate line104 and the source line 105. The region where the pixel electrode 107overlaps with the gate line 104 and the source line 105 becomes a blackmatrix which shields light around the edge of the pixel electrode.

The electrode pattern 106 indicated by the slant lines in FIG. 1 forforming the capacitor also overlaps with the pixel electrode 107indicated by the slant lines in FIG. 2 in the region indicated by ahatched part 109 in FIG. 3.

The auxiliary capacitor is formed in the region where these two ITOelectrode patterns overlap. That is, the auxiliary capacitor which isconnected in parallel with a capacitor formed between the liquid crystaland the counter electrode is formed.

FIG. 4 and below are section views, along a line A-A′ in FIG. 1, showingfabrication steps thereof. FIGS. 9A-9D and 10 are section views showingcorresponding fabrication steps.

At first, as shown in FIG. 9A, a silicon oxide film 902 is formed into athickness of 3000 Å on a glass substrate (or quartz substrate) as anunderlayer film by sputtering. It is noted that a section along a lineB-B′ in FIG. 4 corresponds to the section in FIG. 9A.

Next, an amorphous silicon film not shown is formed into a thickness of500 Å by LPCVD. This amorphous silicon film becomes a starting film forforming an active layer of a thin film transistor later.

After forming the amorphous silicon film not shown, laser light isirradiated. By irradiating the laser light, the amorphous silicon filmis crystallized and a crystal silicon film is obtained. Also, theamorphous silicon film may be crystallized by heating.

Next, the crystal silicon film thus obtained is patterned to form theactive layer 101 whose pattern is shown in FIGS. 4 and 9A. Thesource/drain region and the channel region are formed within the activelayer in the later steps.

Thus, the state shown in FIGS. 4 and 9A is obtained. Next, a siliconoxide film 903 which functions as a gate insulating film is formed intoa thickness of 1000 Å by plasma CVD as shown in FIG. 9B (not shown inFIG. 4).

Next, the gate line 104 is formed as shown in FIG. 5. This gate line 104is made of aluminum. Further, although not clear from the figures, ananodic oxide film is formed on the surface of the aluminum as aprotection film. It is noted that the gate line 104 is not shown in FIG.9 (that is, no gate line exists on the section face in FIG. 9).

Here, the regions of the active layer where the gate line 104 overlapswith the active layer 101 become channel regions. That is, the regionsdenoted by the reference numerals 501 and 502 in FIG. 5 are the channelregions. In case of the present embodiment, there exist two channelregions. It is constructed such that two thin film transistors areconnected equivalently in series.

Such structure allows the backward leak current and the degree ofdeterioration to be reduced because voltage applied to one thin filmtransistor is divided to each transistor part.

After forming the gate line 104, impurity is doped in the state shown inFIG. 5. Here, P (phosphorus) element is doped by plasma doping in orderto fabricate an N-channel type thin film transistor.

In the impurity doping step, the gate line 104 becomes a mask and thesource region 103 and the drain region 102 are fanned in a manner ofself-alignment. The positions of two channel regions 501 and 502 arealso determined in a manner of self-alignment.

After finishing to dope the impurity, laser light is irradiated toactivate the doped element and to anneal damages of the active layercaused during the doping. This activation may be implemented byilluminating by a lamp or by heating.

After forming the gate line 104, a laminate film made of a siliconnitride film 904 and a polyimide film 905 is fainted. This laminate filmfunctions as a first interlayer insulating film. Thus, the state shownin FIG. 9B is obtained.

The utilization of the resin film such as polyimide as the interlayerinsulating film allows the surface thereof to be flattened.

Next, a contact hole 111 is created through the first interlayerinsulating film made of the laminate films 904 and 905 as shown in FIG.9C. Then, the source line 105 is formed as shown in FIGS. 6 and 9C.

The source line 105 is put into a state in which it contacts with thesource region 103 via the contact hole 111. It is noted that the sectionalong a line C-C in FIG. 6 corresponds to that shown in FIG. 9C.

Next, a polyimide film 906 is formed as a second interlayer insulatingfilm as shown in FIGS. 9D and 7.

Further, the pattern 106 made of ITO (for forming the auxiliarycapacitor) is formed. Here, the section along a line D-D′ in FIG. 7corresponds to that shown in FIG. 9D.

Next, a polyimide film 907 is formed as a third interlayer insulatingfilm as shown in FIGS. 8 and 10. Further, the pixel electrode 107 madeof ITO is formed.

Here, the region where the pixel electrode 107 overlaps with the sourceline 105 (and the gate line) functions as the black matrix as describedbefore. Further, regions 908 where the ITO electrode 106 overlaps withthe pixel electrode 107 function the auxiliary capacitor.

Creating the sectional structure as shown in FIG. 10 allows thefollowing significances to be obtained.

(1) By overlapping the edge of the pixel electrode 107 with the sourceline and the gate line, the overlapped region functions as the blackmatrix. Thereby, the aperture ratio may be increased to the maximum.

(2) A required capacity may be obtained without dropping the apertureratio by forming the auxiliary capacitor 908 between the pattern 106made of ITO 908 and the pixel electrode 107. In particular, the degreeof freedom of the ITO pattern to be formed by overlapping with the pixelelectrode may be increased to obtain the required capacity.

(3) As it is apparent from FIG. 10, the ITO pattern 106 for forming theauxiliary capacitor is patterned to have an area greater than the sourceline 105 and is kept at an adequate reference potential. It allows theITO pattern 106 to function also as a shield film for electricallyshielding the pixel electrode 107 from the source line 105. Then,cross-talk between the source line 105 and the pixel electrode 107 maybe suppressed. This effect may be obtained in the same manner alsobetween the pixel electrode and the gate line.

Second Embodiment

The present embodiment relates to a structure modified from that shownin the first embodiment. The source line and the gate line have beenoverlapped with the pixel electrode and the overlap regions have beencaused to function as the black matrix in the structure shown in thefirst embodiment. The structure shown in the first embodiment has beenuseful in increasing the aperture ratio to the maximum. However, it isnecessary to increase the area of the black matrix depending on arequested image quality or a displaying method.

The present embodiment relates to a structure which can be utilized insuch a case. FIG. 11 shows a section of a pixel part according to thepresent embodiment. FIG. 11 corresponds to FIG. 10 and the samereference numerals with those in FIG. 10 denote the same components inFIG. 11.

In the present embodiment, part of a film 1102 which is made of atitanium film or chromium film (or an adequate metallic film) and whichconstitutes the black matrix overlaps with the edge of the pixelelectrode 107 made of ITO.

An ITO pattern 1101 has an area greater than the black matrix 1102 forcovering the black matrix 1102 to increase the value of the auxiliarycapacitor further. The ITO pattern 1101 for forming the auxiliarycapacitor will not drop the aperture ratio even if its area isincreased.

The adoption of the invention disclosed in the present specificationallows the black matrix to be provided without dropping the apertureratio of the pixel. Further, it allows the necessary auxiliary capacitorto be provided without dropping the aperture ratio of the pixel. Stillmore, the cross-talk between the source and gate lines and the pixelelectrode may be suppressed by the electrode pattern forming theauxiliary capacitor with the pixel electrode.

While, preferred embodiments have been described, variations theretowill occur to those skilled in the art within the scope of the presentinventive concepts.

What is claimed is:
 1. A semiconductor device comprising: a transistor comprising a gate, a source and a drain; a first line, wherein a portion of the first line constitutes the gate; a layer comprising a silicon nitride film in contact with the first line; a second line electrically connected to one of the source and the drain; a third line comprising a first portion extending along the first line, and a second portion extending along the second line; a pixel electrode overlapping the third line; and a capacitor comprising the pixel electrode and the third line, wherein the second line is not electrically connected to the third line.
 2. The semiconductor device according to claim 1, wherein the second portion of the third line overlaps with the second line.
 3. The semiconductor device according to claim 1, wherein the first portion of the third line overlaps with the first line.
 4. The semiconductor device according to claim 1, wherein the third line is formed over the first line.
 5. The semiconductor device according to claim 1, wherein the third line comprises ITO.
 6. A semiconductor device comprising: a transistor comprising a gate, a source and a drain; a first line, wherein a portion of the first line constitutes the gate; a layer comprising a silicon nitride film in contact with the first line; a second line electrically connected to one of the source and the drain; a third line comprising a first portion extending along the first line, and a second portion extending along the second line; a pixel electrode overlapping the third line; and a capacitor comprising the pixel electrode and the third line, wherein the first portion of the third line crosses over the second line.
 7. The semiconductor device according to claim 6, wherein the second portion of the third line overlaps with the second line.
 8. The semiconductor device according to claim 6, wherein the first portion of the third line overlaps with the first line.
 9. The semiconductor device according to claim 6, wherein the third line is formed over the first line.
 10. The semiconductor device according to claim 6, wherein the third line comprises ITO. 